by Nancy Mahon, USA TODAY

by Nancy Mahon, USA TODAY

With the recent passing of former surgeon general C. Everett Koop, we have lost a titan in the HIV/AIDS movement in America. While Koop waged numerous public health battles, including an important and unprecedented fight against smoking, I will always remember him best for his pivotal role in leading the American government's response to the HIV/AIDS epidemic.

The AIDS epidemic was just starting in 1981 when Koop was appointed. He was relentless in his efforts to convince the Reagan administration to issue a coordinated response and to educate the American public broadly about safe sex and other risk factors for transmission of the disease. Most of all, Koop was passionate about combating the stigma of HIV/AIDS and not blaming its victims.

I'm proud to say that much has changed in HIV/AIDS since Koop's term as surgeon general. We have been fortunate to witness advancements in medicine and public health that effectively changed the face of the disease from a death sentence to a chronic, but manageable condition.

Much has changed, but not enough. Though countless lives have been saved, far too many are still forgotten: certain at-risk groups, such as poor, urban African-American women, have HIV rates that rival those of some countries in sub-Saharan Africa.

While great attention has been paid to the importance of raising awareness of the disease and ensuring access to treatment we are still not reaching many of the most vulnerable people and there is still another major gap in the care continuum: retention in care.

A recent Centers for Disease Control and Prevention study found that less than half the people in the U.S. who are tested and start treatment for HIV stay on treatment, and only a third of those that stay on treatment manage their disease as well as they could. Those are pretty lousy odds.

Staying in care is critically important because contemporary research shows that people on treatment are less likely to transmit the virus to their partners -- meaning that proper treatment can serve as an active method of prevention. Importantly, if people are unable to have sustained access or don't stay on their medication, then the benefits that care and treatment offer are lost.

The environment is ripe to reverse these statistics in the U.S. Implementation of the Affordable Care Act offers hope for the HIV community by extending health insurance coverage to many Americans for the first time and expanding Medicaid to those with lower incomes who are often hit hardest by HIV and least likely to start or stay on treatment.

On the other hand, the ACA also means that many people who have been following the same HIV treatment processes for years will now need to navigate a whole new system of insurance claims, new doctors and in many places, fewer choices in medications. Furthermore, many people in the U.S. will still not qualify for, or seek out, insurance coverage, including some of those disproportionately affected by the disease.

In addition to the ACA, under President Obama's leadership, we have for the first time a National HIV/AIDS strategy aimed at achieving an AIDS-free generation. The challenge, however, is making sure this ambitious plan actually impacts the hardest-to-reach populations.

Simply put, we are not going to be able to end the epidemic in the U.S. without focusing on the groups typically marginalized and underserved by traditional health care in our country -- groups who represent the lion's share of the disease burden.

Koop understood this reality. Yet now, more than two decades later, we still don't have a safety net to link people to care and keep them enrolled in treatment. A handful of private donors have followed Koop's lead. We are squarely focused on supporting those who need care the most and who are at the highest risk of dropping out of care, including men who have sex with men, African-American women, transgendered individuals and injecting drug users.

This is a critical time for HIV/AIDS in the U.S. We must ensure that all Americans have access to health insurance and life-saving care, and that funding for many of these critical health programs is preserved. But allocating resources is not enough. It is essential that we utilize these resources more wisely and direct them at model programs that have successfully shown to help prevent new HIV infections or keep people enrolled in treatment. Only then can we fully achieve Koop's vision and realize the end of the AIDS epidemic in the U.S.

Nancy Mahon is global executive director of M·A·C AIDS Fund and chair of the Presidential Advisory Council on HIV/AIDS.

In addition to its own editorials, USA TODAY publishes diverse opinions from outside writers, including our Board of Contributors.